diff --git a/internal/handlers/opds.go b/internal/handlers/opds.go
index 7b5d286..9b5d34b 100644
--- a/internal/handlers/opds.go
+++ b/internal/handlers/opds.go
@@ -605,6 +605,12 @@ func (h *OPDSHandler) DownloadBook(c *echo.Context) error {
 		if mediaItem.MimeType.Valid {
 			mimeType = mediaItem.MimeType.String
 		}
+		// Always expose the primary content hash so clients (e.g. the koreader
+		// plugin) learn the canonical SHA-256 from the download response itself,
+		// not just from the feed metadata.
+		if mediaItem.FileSha256.Valid {
+			fileSha256 = mediaItem.FileSha256.String
+		}
 	}
 
 	// Check if file exists